Maybe the normally-closed type would fit better. But then you need a voltage and current to break the whole circuitry. Using the normally-open type will break the circuitry if voltage or current get lost. This looks for me as a safer solution. Power consumption to keep the normally-open type closed does not seem to be very high: 1.5W from the datasheet.
Precharge was described in this topic: Precharge circuit - Expansion board settings - #2 by James
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